1. Technical Field of the Invention
The principles of the present invention are generally directed to a light bulb, and more particularly, but not by limitation, to a light bulb using electronic light generating elements, such as LEDs, and having circuitry for over-driving the electronic light generating elements to produce a perceived higher amount of light.
2. Description of Related Art
Since the invention of the light bulb by Edison, light bulbs have become pervasive throughout society. Light bulbs have evolved for all sorts of uses as technology for generating light has developed. Initially, an incandescent light bulb that uses a metal filament placed inside a glass bulb forming a vacuum was developed. The incandescent light bulb operates by driving current through the filament to cause the filament to heat up and produce light. While the incandescent light bulb is effective in producing large amounts of light, these light bulbs are very inefficient in that a substantial portion of the energy used to generate the light is immediate converted into heat. The inefficient use of energy is expensive and the resulting heat is generally undesirable as it can cause an individual handling the lit light bulb to receive a burn injury, especially with higher wattage light bulbs. In applications where many incandescent light bulbs are used to illuminate an occupied space (e.g., casinos, malls, retail environments, work environments, etc.), additional cooling is needed to maintain a comfortable temperature for people within that setting due to the heat produced by the lighting. Another limitation of a conventional incandescent light bulb is its limited life span. The life span problem is particularly problematic in applications where the light bulb is not readily accessible, such as in high locations or in complex fixtures, and requires manual labor and/or machine support for changing the light bulb. For example, changing traffic light bulbs, particularly those suspended from wires or located at a higher elevation, is a particularly difficult and expensive task as it requires both labor and a specialized vehicle having a lift for raising someone to a height of the traffic light to change the light bulbs.
A light emitting device developed after the incandescent light bulb is a fluorescent light emitting device. Fluorescent light is generally produced by creating electric arcs inside a gas-rich tube to produce ultraviolet light. The ultraviolet light is converted to visible light by passing the ultraviolet light through a layer of phosphor on the inside of the glass tube to cause the phosphor to glow white. Fluorescent lights have traditionally been produced in tubes having an electrode at each end for creating the electric arcs within the gas filled tube. However, more recently, fluorescent light bulbs have been developed to be compatible with an Edison-based socket and shaped as a light bulb. While the fluorescent light bulb is an improvement of the incandescent light bulb in terms of having a longer life span, the use of the fluorescent light bulb is still commercially limited due to a number of factors, including: objectionable color, efficiency concerns, limited configurations, environmental concerns, and limited life spans.
More recently, solid-state light emitting devices have been developed for light bulbs and flashlights. One such solid-state light emitting device is a light emitting diode (LED). LEDs overcome many of the problems that are found in incandescent and fluorescent lighting systems. LEDs are more durable, do not require a glass vacuum, produce significantly lower heat than any non-solid state lighting devices, and, thus, have a longer life span. However, LEDs have certain limiting factors and, thus, have not been commercially viable for general purpose lighting. Such limitations include narrow illumination beam widths at higher efficiency outputs, ultra-narrow frequency bandwidths, and lower luminance output.
Light emitting diodes are solid-state devices and produce light when an electric current passes through the device and causes electrons to recombine with holes, thereby emitting photons at a PN junction of two differently doped substrates, one negatively charged (N-type substrate) and one positively charged (P-type substrate). When current is applied to the LED and flows across the PN junction, the junction heats up. If a current exceeds a maximum specified forward current for a long enough duration of time, as defined by a manufacturer of the LED, a catastrophic failure causing complete or partial damage to the functionality of the LED may result.
To increase the brightness of LEDs while lowering the temperature of the PN junction, manufacturers of LEDs have spent much research and development time and money in producing different heat sinks and materials. Reducing the PN junction temperature improves performance of an LED as more current can be applied to the LED to produce more light without burning out the LED. While the performance of the LED has greatly improved by the use of different materials, users of LEDs must drive the LEDs within a manufacturer's specification to avoid damaging them in whole or part. The limiting factor of LED operation is the PN junction temperature. So as to not burn out an LED, the conventional technique for powering an LED includes applying a DC current below a maximum (average) forward current, which is the maximum average amount of current the LED is able to conduct in a forward bias mode. The maximum forward current for typical LED devices is about 20–30 milliamps (mA), though it may vary beyond this range. In the case of the maximum forward current being 20 mA, for direct current (DC) applications to produce a maximum illumination from the LEDs, a DC current of 19.5 mA may be used. While this technique is effective in minimizing burnout to protect the LEDs, the limited amount of luminance produced by this technique is not necessarily satisfactory for many applications using an LED light bulb. To increase the amount of illumination of the LED light bulb using a DC driving technique, manufacturers increase the number of LEDs within a single bulb structure. While the increased number of LEDs improves the light intensity of the overall light bulb, it also increases cost and size of the LED light bulbs, thereby reducing commercialization potential of the LED light bulb.
In order to reduce the thermal problems of the PN junction of the LED devices, some manufacturers have used pulse width modulation (PWM) to drive the LEDs. Pulse width modulation is a technique for driving a signal that alters the width of a pulse to change a duty cycle (i.e., ratio of ON time to OFF time within a period). By using a duty cycle less than 100 percent as is the case of using the DC driving technique, the PN junction temperature may be reduced. The human eye is generally incapable of noticing flicker of a light strobing at or above 100 pulses per second. The pulse width modulation driving technique typically operates at 100 Hz maintains a duty cycle of 30 and 60 percent or higher. This reduced duty cycle from the DC driving technique, which has a 100 percent duty cycle, maintains a lower PN junction temperature. While using pulse width modulation is an inexpensive way to convert AC light bulb applications to DC light bulb applications, the LED brightness remains limited by the PN junction temperature. In other words, by using pulse width modulation, an effective average current results such that the PN junction temperature remains below a thermal temperature that causes the LEDs to catastrophically fail. Pulse width modulation driving devices are widely available and serve as a good midpoint solution. However, as the duty cycle employed in pulse width modulation driving techniques exceed peak current ratings of LED manufacturers by 200 to 600 percent, pulse width modulation supplies and/or drivers cannot drive the LED to their maximum output without encountering the same failure mode associated with DC supplies.
Manufacturers of white LED light bulbs typically use blue or ultraviolet LEDs for generating light and use a phosphor coating on the lenses or above the wafer of the LEDs to produce visible white light similar to a fluorescent light bulb. However, such a configuration causes a loss of output efficiency because phosphor tends to backscatter the light produced by the LEDs. Also, the life of the LED light bulbs with phosphor is diminished because phosphor has a more limited life expectancy than the underlying light emitting diode. Finally, as with the fluorescent light bulb, color of the produced light is objectionable from a commercial standpoint and degrades over time.
A structural disadvantage of conventional LED light bulbs results from the use of transformers as a DC power source for driving the LEDs with a lower voltage. The use of the transformer requires the use of a large base for the LED light bulb, thereby making the conventional LED light bulbs incapable of fitting into a conventional light socket and/or having a less appealing appearance to consumers.